1. Field of the Invention
The present invention relates to a pad layout structure of a driver IC (integrated circuit) chip in a liquid crystal display, and more particularly, to a pad layout structure of a driver IC chip in which, when mounting a driver IC chip to a liquid crystal display panel in a chip-on-glass (COG) type, power pads of the driver IC chip are located at the corners of the driver IC chip in all four directions so that the adhesion between the driver IC chip and the liquid crystal display panel can be enhanced.
2. Description of the Related Art
A liquid crystal display (LCD) indicates a device in which image data is displayed by passing light rays through liquid crystal based on the fact that the alignment of liquid crystal molecules is changed depending upon an applied voltage. Among LCDs, a thin film transistor (TFT) LCD, which is manufactured using technology for manufacturing a silicon integrated circuit, is most widely used these days.
FIG. 1 is a view schematically illustrating the structure of a conventional liquid crystal display.
A TFT LCD comprises a liquid crystal display panel 30 in which a thin film transistor array substrate and a color filter substrate facing each other are bonded to each other with a predetermined space defined therebetween and liquid crystal is injected into the predetermined space, and a driving circuit for driving the liquid crystal display panel 30.
The driving circuit includes a gate driver integrated circuit 40 which sequentially applies scanning signals to gate lines every frame, a source driver integrated circuit 20 which drives source lines in response to the scanning signals from the gate driver integrated circuit 40, a timing control section 10 which controls the gate driver integrated circuit 40 and the source drive integrated circuit 20 and outputs pixel data, and a power supply section (not shown) which supplies various driving voltages to be used in the LCD.
In general, a method for connecting the driver integrated circuit with the liquid crystal display panel is divided into a tape automated bonding (TAB) type in which the driver integrated circuit is mounted on a thin contractible film made of a polymeric material, that is, a tape carrier package (TCP), and the thin contractible film is connected with the liquid crystal display panel so as to electrically connect the driver integrated circuit with the liquid crystal display panel, and a chip-on-glass (COG) type in which the driver integrated circuit is directly mounted to the glass substrate of the liquid crystal display panel using bumps.
Although the TAB type has been widely used in the past in that adhesion is excellent and TAB can be easily modified, the COG type is recently gaining popularity in that COG is advantageous for miniaturization and the manufacturing cost is low.
COG means a method in which the output electrodes of the driver integrated circuit are directly connected to pads so that the substrate and the driver integrated circuit are integrated with each other. In the COG type, when conducting a process for bonding the bumps and the pads, the bumps and the pads are bonded to each other by the medium of conductive particles which are placed therebetween.
In the COG type, the signal lines of the chips of the driver integrated circuits, which are mounted to the liquid crystal display panel, are connected with each other in a line-on-glass (LOG) type in which the signal lines are directly mounted to the thin film transistor array substrate. The chips of the driver integrated circuits are supplied with control signals and driving voltages from the timing control section and the power supply section.
FIG. 2 is a view illustrating a pad layout structure of a driver IC chip which is mounted in a COG type according to the conventional art.
Referring to FIG. 2, it is the norm that a driver IC (integrated circuit) chip has a rectangular shape in which the length thereof in the transverse direction is greater than the length thereof in the longitudinal direction due to the application characteristic of the LCD.
In a driver IC chip 200 which is mounted in a COG type according to the conventional art, an internal circuit 210 is centrally placed, an input pad section 220 is placed adjacent to the upper side edge of the chip 200, and an output pad section 230 is placed adjacent to the lower side edge of the chip 200. Besides, in the driver IC chip 200, there should be placed power supply lines 251 and 252 and power pads 241a through 241d and 242a through 242d. 
In the case where not only the internal circuit, the input pad section and the output pad section but also the power supply lines and the power pads are all designed in the driver IC chip, the size of the panel, to which the driver IC chip is to be mounted, should be increased, and accordingly, a required amount of glass is also increased.
Therefore, in the conventional art, when designing a source driver IC chip and a gate driver IC chip, in order to decrease the area occupied by the power lines and the ground lines of the driver IC chip, power pads and ground pads are placed adjacent to the input pad section of the driver IC chip or at the left or right end portion A of the driver IC chip.
When the power pads and the ground pads are placed adjacent to the input pad section of the driver IC chip or at the left or right end portion A of the driver IC chip, if the force applied for bonding is not uniform at the corners of the driver IC chip in four directions, the driver integrated circuit is likely not to operate normally.
That is to say, in the case where the power pads and the ground pads are placed only at the position of the input pad section, if the force applied to the input pad section for bonding is greater than the force applied to the output pad section for bonding, the bonding force of the output pad section becomes insufficient, which can lead to poor image. Conversely, if the force applied to the output pad section is greater than the force applied to the input pad section, the bonding force of the power pads and the ground pads becomes insufficient, which can cause various problems such as image noise and defective frequency reception.
As a result, in the source driver IC chip and the gate driver IC chip according to the conventional art, due to the fact that the power pads and the ground pads are placed at one side of the chip, when the force applied to the chip for bonding is not uniform, problems such as poor image and defective frequency reception can be caused.